144 lines
5.0 KiB
ReStructuredText
144 lines
5.0 KiB
ReStructuredText
=======================
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Keyboard/Keypad Drivers
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=======================
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**Keypads vs. Keyboards** Keyboards and keypads are really the
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same devices for NuttX. A keypad is thought of as simply a
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keyboard with fewer keys.
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**Special Commands**. In NuttX, a keyboard/keypad driver is simply
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a character driver that may have an (optional) encoding/decoding
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layer on the data returned by the character driver. A keyboard may
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return simple text data (alphabetic, numeric, and punctuation) or
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control characters (enter, control-C, etc.) when a key is pressed.
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We can think about this the "normal" keyboard data stream.
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However, in addition, most keyboards support actions that cannot
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be represented as text or control data. Such actions include
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things like cursor controls (home, up arrow, page down, etc.),
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editing functions (insert, delete, etc.), volume controls, (mute,
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volume up, etc.) and other special functions. In this case, some
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special encoding may be required to multiplex the normal text data
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and special command key press data streams.
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**Key Press and Release Events** Sometimes the time that a key is
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released is needed by applications as well. Thus, in addition to
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normal and special key press events, it may also be necessary to
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encode normal and special key release events.
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**Encoding/Decoding** Layer. An optional encoding/decoding layer
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can be used with the basic character driver to encode the keyboard
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events into the text data stream. The function interfaces that
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comprise that encoding/decoding layer are defined in the header
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file ``include/nuttx/input/kbd_code.h``. These functions provide
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an matched set of (a) driver encoding interfaces, and (b)
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application decoding interfaces.
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#. **Driver Encoding Interfaces**. These are interfaces used by
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the keyboard/keypad driver to encode keyboard events and data.
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- ``kbd_press()``
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**Function Prototype:**
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**Description:**
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**Input Parameters:**
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- ``ch``: The character to be added to the output stream.
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- ``stream``: An instance of ``lib_outstream_s`` to perform
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the actual low-level put operation.
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**Returned Value:**
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- ``kbd_release()``
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**Function Prototype:**
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**Description:**
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**Input Parameters:**
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- ``ch``: The character associated with the key that was
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released.
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- ``stream``: An instance of ``lib_outstream_s`` to perform
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the actual low-level put operation.
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**Returned Value:**
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- ``kbd_specpress()``
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**Function Prototype:**
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**Description:**
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**Input Parameters:**
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- ``keycode``: The command to be added to the output
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stream. The enumeration ``enum kbd_keycode_e keycode``
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identifies all commands known to the system.
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- ``stream``: An instance of ``lib_outstream_s`` to perform
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the actual low-level put operation.
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**Returned Value:**
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- ``kbd_specrel()``
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**Function Prototype:**
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**Description:**
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**Input Parameters:**
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- ``keycode``: The command to be added to the output
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stream. The enumeration ``enum kbd_keycode_e keycode``
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identifies all commands known to the system.
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- ``stream``: An instance of ``lib_outstream_s`` to perform
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the actual low-level put operation.
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**Returned Value:**
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#. **Application Decoding Interfaces**. These are user interfaces
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to decode the values returned by the keyboard/keypad driver.
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- ``kbd_decode()``
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**Function Prototype:**
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**Description:**
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**Input Parameters:**
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- ``stream``: An instance of ``lib_instream_s`` to perform
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the actual low-level get operation.
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- ``pch``: The location to save the returned value. This
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may be either a normal, character code or a special
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command (i.e., a value from ``enum kbd_getstate_s``.
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- ``state``: A user provided buffer to support parsing.
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This structure should be cleared the first time that
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``kbd_decode()`` is called.
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**Returned Value:**
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- ``KBD_PRESS`` (0)**: Indicates the successful receipt
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of normal, keyboard data. This corresponds to a keypress
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event. The returned value in ``pch`` is a simple byte of
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text or control data.
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- ``KBD_RELEASE`` (1)**: Indicates a key release event.
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The returned value in ``pch`` is the byte of text or
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control data corresponding to the released key.
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- ``KBD_SPECPRESS`` (2)**: Indicates the successful
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receipt of a special keyboard command. The returned value
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in ``pch`` is a value from ``enum kbd_getstate_s``.
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- ``KBD_SPECREL`` (3)**: Indicates a special command key
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release event. The returned value in ``pch`` is a value
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from ``enum kbd_getstate_s``.
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- ``KBD_ERROR`` (``EOF``)**: An error has getting the
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next character (reported by the ``stream``). Normally
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indicates the end of file.
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**I/O Streams**. Notice the use of the abstract I/O streams in
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these interfaces. These stream interfaces are defined in
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``include/nuttx/streams.h``.
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